Seal Oil & Gas Flashcards
Describe the Hydrogen Cooling System.
- Main generator housing is pressurized to 74-80 psig Hydrogen during normal operation
o Minimum pressure for full power operations 69 psig.
o <70 psig for initial pressurization to allow system heatup - Hydrogen has better Thermal Conductivity and less Windage losses than air
- Where the shaft penetrates the housing there is a Hydrogen Seal Ring
- H2 circulated through the generator and H2 cooler by a blower attached to the generator shaft
- TCW is supplied to the H2 cooler for heat removal
- Hydrogen dryer
o Powered by MCC 1A1 [2A1]
o {U1
Dual tower unit for continuous drying of hydrogen gas.
Utilizes regenerative type dessicant
Fully automatic, requires no manual regeneration.
Uses heat from embedded electric heaters to regenerate the dessicant columns.
Tower swapping occurs at system pressures.}
o [U2
Alarms at +45oF
Light blue = dry, Pinkish gray = wet] - Hydrogen purity
o High and Low purity alarms at 100% and 90%
Describe Generator Gas Temperature Monitoring.
24 Hot Gas RTDs (H2 exiting Stator core).
4 Cold Gas RTDs (H2 exiting H2 Coolers).
RTDs located in H2 Gas stream indicative of winding temperatures.
High Temps indicate internal failure.
Abnormal Temp gradients or hot spots can cause differential expansions and damage.
Powered from 120 VAC Vital SUPS
Monitors:
o Generator Load
o Hot Gas Temps
o Cold Gas Temps
o Hydrogen Press
o Differential Temps
o Trends on recorders
Describe Generator Core Condition Monitor.
Overheating Main Generator causes insulation to break down.
Lead to complete failure.
Detects insulation particles released into H2.
Low current flow in ion chamber due to insulation particles triggers alarm
o If bypassing filter clears alarm, indicates an issue.
Describe the Seal Oil System.
Air side is provided with seal oil from the Air Side Seal Oil Pump MCC 1C [2C]
o Seal oil is provided to maintain the DP at 12 psid to prevent escape of Hydrogen
o If D/P between H2 gas and air side seal oil decreases to:
8 psid
Backup source of seal oil from the Main Lube Oil System, Regulator
o Main Turbine shaft drives Main Turbine Oil
o Seal Oil BU pump (Powered from MCC 1A1 [2B1]) auto starts 9.5 to 13.5 psig (Same as Bearing Oil Pump) on the #6 Main Turbine bearing
5 psid
Air Side Seal Oil BU Pump 125 VDC 1D [2D] will Auto Start
Generator/Hydrogen side is provided with seal oil from Hydrogen Side Seal Oil Pump
o Hydrogen Side Seal Oil Pump can be kept out of service indefinitely provided that sufficient Hydrogen is added to the Main Generator to maintain purity
o Hydrogen side Seal oil pump is MCC 1C [2C] powered.
Describe Hydrogen & Air Side Seal Oil Coolers.
- Each cooled by TCW with its own TCV
- Maintain temp out of both heat exchangers within 2F of each other or the Hydrogen seal Ring starts to chatter due to the uneven temperature distribution
Describe Scenarios affecting Seal oil.
SBO
* Air side seal oil backup pump running to supply H2 seal oil @ nominally 75 psig
* HP seal oil backup, MLO, BOP, Lift pump, H2 side seal oil pump all have no power.
* H2 side seal oil pressure will be 0 psig.
Lowering pressure
* High pressure TLO would supply at 8 psid between air side seal oil and H2 gas pressure
* Air side seal oil backup (DC) would start at 5 psid
* Low pressure lube oil would supply to maintain ~2 psig of H2 in generator if all other seal oil is lost.
Describe Seal Oil System Startup.
- If the system is drained, system is filled from HP lube oil through backup regulator.
- When normal oil level is available TCW is established to the oil coolers.
- The air side seal oil pump is started.
- Then the hydrogen side seal oil pump is started.
- Then the generator bearing oil vapor extractor is started.
- Once seal oil is operating properly, the generator is purged of air.
- CO2 is admitted until the generator contains 95% CO2 by volume.
- Chemistry sample is used to verify concentration.
- After Air is purged by CO2, H2 can then be safely admitted to the generator without creating a fire or explosion hazard.
- H2 is admitted until the generator contains 95% hydrogen by volume.
- Chemistry sample is used to verify concentration.
Describe Seal Oil Normal Operation.
- Seal oil System should be in operation whenever H2 gas is in the generator or shaft is turning.
- 1[2]-NOP-22.02 provides instructions for normal seal oil operations.
- 1[2]-NOP-22.01 provides instructions for normal generator gas operations
- H2 pressure is maintained by manual makeup.
- H2 is controlled by feed and bleed.
Describe Seal Oil Abnormal Operation.
- 1[2]-AOP-53.01, Main Generator, provides mitigating actions for abnormal generator conditions
- If a complete loss of seal oil occurs with hydrogen in the generator, hydrogen would leak from the generator presenting a fire hazard
- High Gas Temperature could be caused by one or more of the following:
o Low hydrogen purity
o Low hydrogen pressure
o Loss of hydrogen cooling (TCW)
If not restored, plant load is reduced to prevent damage to the main generator due to overheating. System Dispatch may have to be notified in 30 minutes. - Some conditions may require Unit Trip
- Local operator actions may be required to restore parameter
- Seal Oil can maintain H2 pressure even with a complete loss of H2 side seal oil.
- Increased additions or feed and bleeds would be required to maintain purity
- Hydrogen Panel Annunciators
Trips are required (at present) on
Low Hydrogen Pressure, {30} [45] psig
Hot Gas Avg temp HI (113ºF)
Max Hot Gas ΔT
{Unit 1 has all 24 temperatures looked at in Max to Min (See curve)}
[Unit 2 has Max Hot Gas ΔT LS and RS]
Describe Seal Oil System Shutdown.
- H2 in the generator is vented to the atmosphere.
- Seal oil maintained when turbine on turning gear or pressure maintained in the generator.
- This is followed by adding CO2 until 95% concentration is reached.
- Gas pressure is maintained low to reduce mixing of gases
- At this point dry air can be safely added to the generator.
- When the generator shaft is stopped, the seal oil system can be secured.
- The backup regulator is isolated to prevent auto makeup.
- The breaker for the air side backup pump is open to prevent auto starting.
- Then the air side seal oil pump is stopped.
- If the vapor extractor is to be stopped, the bearing oil pump will have to be stopped to prevent oil from leaking out the generator bearings.
Describe Seal Oil “need to know information”.
- H2 pressure 74 to 80 psig
- H2 Side Seal Oil Pressure > Air Side Seal Oil Pressure results in H2 pressure decreasing
- Air Side Seal Oil Pressure > H2 Side Seal Oil Pressure results in H2 purity decreasing
- Operating band is +/- 2”H20 DP between Air Side and Hydrogen Side Seal Oil Pressures
- Air Side Seal Oil Pressure:
1. Normally 12 psig above Generator H2 presssure maintained by PCV in Seal Oil system.
2. Failure of Air Side Seal Oil Pump results in Air Side Seal Oil pressure being 8 psig above Generator H2 pressure by Backup Regualtor (PCV) supplied by Main Oil Pump online or Seal Oil Backup Pump (AKA HP Seal Oil Backup Pump) if turbine tripped.
3. Failure of all of the above OR Loss of Offsiite Power results in Air Side Seal Oil Backup Pump starting at 5 psid, and Air Side Seal Oil Pressure being maintained 5 psig above Generator H2 pressure.
If all 3 are lost, shutdown unit, vent H2 to less than 2 psig. - Air Side Seal Oil Backup Pump: Powered from 1D[2D] 125 VDC Bus
- TCW cools Seal Oil. Separate TCV’s for H2 Side Seal Oil and Air Side Seal Oil. Operating band is +/- 2F of each other.
- Duplex filters for Air Side and H2 Seal Oil (Separate set for each).
What is the function of the Generator Gas System?
The Generator Gas System provides cooling for the rotor windings, stator windings, and other current carrying components of the main generator.
What is the function of the Seal Oil System?
Maintains a pressure boundary around the generator shaft to prevent the hydrogen (H2) from leaking out of the generator.
Describe the Generator Seal Ring.
- 1 seal package at each end of generator (where turbine shaft enters the generator)
- Two grooves in each ring – which receives inputs from both an Air Side & H2 side seal oil source.
- Both the Air Side & H2 Side seal oil pressures are maintained within +/- 2” H20
Describe the Seal Oil System.
- Designed to maintain seal oil pressure slightly above hydrogen pressure
- Seal oil is provided to maintain the DP at ~ 12 psid to prevent escape of Hydrogen
- Divided into air side and hydrogen side subsystems
